The cell cycle

How often do intestinal epithelial lining cells divide?

Every 5 days by cell division.

Why do liver cells divide?

To repair damage, and then they stop dividing.

Why and how often do bone marrow cells divide?

They divide rapidly to produce red and white blood cells.

Why do meristem cells divide?

Divide to produce new growth (tips of roots and shoots).

Why do cambium cells divide?

To form vascular tissue.

Can specialised cells go through the cell cycle multiple times?

No- they usually only go through the cycle once and then can’t divide again (e.g. nerve cells).

What are the 2 types of cell division and what are they used for?

1. Mitosis- making new cells for growth and repair.

2. Meiosis- formation of gametes.

What are the stages of the cell cycle?

1. G0

2. Interphase- G1, S, G2

3. Mitosis- Prophase, Metaphase, Anaphase, Telophase

4. Cytokinesis

What is G0?

The stationary phase. Some cells never need to replicate again so enter this stage.

What are 2 reasons why a cell may enter stationary phase?

• A cell differentiates and becomes specialised for a certain function indefinitely so can’t divide.

• Cells can only divide a certain amount of times then become senescent (damaged). As you age, more cells become senescent which can lead to cancer and arthritis.

What happens during G1? (5) How long is it? What is the DNA content?

The first growth phase- longest stage

• Protein synthesis

• Cells grow

• Most organelles are produced

• Volume of cytoplasm increases

• Cell differentiation

• DNA content = 46

What happens during S phase? What is the DNA content?

• DNA replicates ready for mitosis

• DNA content = 92

What happens during G2? (2) How long is it? What is the DNA content?

Second growth phase- short gap before mitosis

• Cytoskeleton of the cell breaks down

• Protein microtubule components start to reassemble into spindle fibres ready for division.

• DNA content = 92

What happens during cytokinesis?

The cell divides into 2.

What are the 3 checkpoints in the cell cycle?

• G1

• G2

• Spindle assembly (metaphase)

What happens at the G1 checkpoint?

Checks for cell size, nutrients, growth factors and DNA damage.

Either:

• The cells progress to DNA synthesis

• The cells return to G0

• Apoptosis- programmed cell death

What happens at the G2 checkpoint?

Checks for cell size, DNA replication and DNA damage

Either:

• Triggers molecular process that signals the start of mitosis

• Apoptosis

What happens at the spindle assembly checkpoint?

Checks for chromosome attachment to spindle fibres. If they haven’t attached properly, mitosis can’t proceed.